Conventionally, an electrophotograph-type color-image forming method has been often used as a method for forming a color-image on a recording paper. The electrophotograph-type color-image forming method develops an electrostatic latent image formed on a latent image carrier by a developing device and the image formed on the latent image carrier by developer is finally transferred to paper fed.
A generally used color-image forming device employs the above method is an image forming device which (a) includes a plurality of latent image carriers in order to prevent deceleration of image forming speed, (b) uses different color materials as developer for the respective latent image carriers and (c) forms a color-image by superimposing images formed on the respective latent image carriers.
However, in recent years, many studies have been made to develop intermediate-transfer-type image forming devices in order to deal with varieties of sheets. The intermediate-transfer-type image forming devices do not transfer an image to a recording sheet directly from the latent image carrier, but ultimately transfers, to the recording sheet, a color image formed by superimposing images on the intermediate transfer member to which the images are temporary transferred. (For example, refer to the Japanese Laid-Open Patent Publication 209232/2001 (Tokukai 2001-209232 published on Aug. 3, 2001); corresponding U.S. Pat. No. 6,389,260 and the Japanese Laid-Open Patent Publication 154445/2001 (Tokukai 2001-154445 published on Jun. 8, 2001))
As an image forming device that employs an intermediate transfer system like this, a so-called tandem image forming device is generally used. Though there may be some difference in layout, the tandem image forming device, as illustrated in FIG. 8, is provided, along an intermediate transfer belt 304, with (i) an intermediate transfer belt 304 tensioned by tension rollers 302 and 303 between the rollers 302 and 303, which is used as a intermediate transfer, and (ii) plural image forming stations Pa, Pb, Pc, and Pd, which form images by respective different Color materials.
However, in spite of its high image forming speed, the conventional tandem image forming device has a problem in that a size of the device becomes large due to a large number of component parts.
Specifically in an intermediate-transfer type image forming device as in FIG. 8, an image formed at each image forming stations Pa, Pb, Pc, and Pd goes through the following processes: a) a primary transfer process where the image is temporarily transferred to an intermediate transfer belt 304 from photosensitive drums 222a, 222b, 222c, and 222d that are latent image carriers and b) a second transfer process where the image after the primary transfer process is transferred to recording paper P from the intermediate transfer belt 304. Thus, the image forming device including four latent image carriers as in FIG. 8 has five transfer processes because the primary transfer processes whose number of times is equivalent to the number of photosensitive drums 222a, 222b, 222c, and 222d and the second transfer process (a transfer process for transferring the images together at once) are carried out. Further, the respective image forming stations Pa, Pb, Pc, and Pd should be arranged such that the photosensitive drums 222a, 222b, 222c, and 222d and the intermediate transfer belt 304 are respectively provided with five cleaning devices (cleaning devices 226a, 226b, 226c, 226d and 221 in FIG. 8) for removing residual developer, which is not transferred but left over (remained). Accordingly, this causes a problem in that (a) the device tends to be large in size and (b) production cost increases due to a large number of component parts.